Epidemiology: 15) Control Selection - Secondary Study Base
Terms
undefined, object
copy deck
- Major problem for controls in secondary study base
- If the Probability of being a control differs for the E+ and E- groups, then the measures of effect will be biased (SELECTION BIAS)
- 4 common methods for control selection in a seconday study base
- 1)population lists. 2)neighborhood controls. 3)Random-digit dialing. 4)Hospital controls
- Control selection and population lists
- If lost participants from the population list then there is SELECTION BIAS. Eg. (of 1330 eligible controls only 998 participated)
- Neighborhood controls
- Study base is divided into mutually exclusive neighborhoods where all cases are from. Controls are randomly sampled from the neighborhood of each case at the time disease is diagnosed.
- When best to use neighborhood sample
- 1) recent or current disease identification. 2) Sufficient exposure variation within neightborhoods.
- Disadvantages of Neighborhood samples
- Lack of exposure variation loses statistical efficiency
- Random Digit Dialing
- Random numbers likely within secondary study base. Strict procedures for qualifying controls. Keep track of tries to get control
- Problems with random dialing
- 1) Subjects without phones. 2) Correspondence between telephone numbers and persons. 3) Nonresponse.
- Hospital controls - timing
- Cases are identified continuously in real-time so controls can be selected from patients in the hospital at the same time as cases.
- Identifying hospital controls
- Disease should NOT have the probability of admission related to E. To reduce this some use several diseases
- Biggest mistake for hospital controls
- Using the same organ system to "make controls like the cases"
- When and How to initiating procedures for hospital controls
- Start when a case is identified, have a defined procedure, keep track of tries.
- Hospital controls and index date
- Tx is set at oset of the symptoms for the disease and a comparable time for the controls
- 4 advantages for hospital controls
- 1) Convenience. 2) High participation rates (especially for acute diseases). 3) Controls in hospital likely to have same source of information bias (have the same data). 4)Same access to medical care.
- 2 ways hospital controls are valid
- 1) Treatment and referral patters are same for control and case diseases (often in network of hospitals). 2) Control diseases not associated with exposure.
- 3 Althernative control selection methods
- 1) Medical practice controls. 2)Friend or relative control. 3) Controls outside study base.
- Medical practice controls
- Managed care patients. Can lead to bias (eg. caffeine and colon cancer)
- Advantages of Friend/Relative control
- 1) Convenient. 2) Possibly Reduce social class bias
- Disdavantages of Friend/Relative control
- 1) Does not meet study base principle. 2) Differential selection related to exposure is likely
- Controls from ouside study base
- Comparable to using historical controls in CT or external E-
- Multiple control groups
- Try to reduce bias. Usually a dark alley (what if results differ between the groups!)